Used to be cut back (3)
I believe the answer is:
was
'used to be' is the definition.
(I've seen this before)
'cut back' is the wordplay.
'cut' becomes 'saw' (sawing is a kind of cutting).
'back' says the letters should be written backwards.
'saw' written backwards gives 'WAS'.
(Other definitions for was that I've seen before include "(I/he) existed" , "Is no longer" , "Lived" , "'Is, in the past (3)'" , "(He/she/it) existed" .)